Generator delegation via yield from

In PHP 7, generator delegation allows you to yield values from another
generator, Traversable object, or
array by using the yield from keyword.
The outer generator will then yield all values from the inner generator,
object, or array until that is no longer valid, after which execution
will continue in the outer generator.

If a generator is used with yield from, the
yield from expression will also return any value
returned by the inner generator.